iMac - iTunes problem

I have a 'volleyball' G4 iMac and have been experimenting using it and other sources to drive a Sonic Impact T-amp that I'd repackaged into a new enclosure with a good quality volume pot and connectors.

From iTunes on the iMac, with the amp plugged into the headphone jack, the sound of mp3's has considerable high-frequency distortion, or that's what it sounds like. There's a staticy, sibilant sound that's quite irritating.

The same mp3's copied to an Archos jukebox and then played through exactly the same amp and speakers sound fine. They sound great, in fact, the T-amp is quite a wonderful little piece of gear. A regular CD player plugged into the same system also sounds wonderful.

So, the question: Is there something wrong with my particular iMac or is the internal DAC and amplification of the iMac just of lower quality than that in the other sources?

If the latter is the case, can I bypass the iMac internal system by using a USB digital connection like the Waveterminal? I love the convenience of iTunes combined with the T-amp but the quality just isn't acceptable as is.

I'd appreciate hearing about your experience and suggestions.
Using the iMac's own DAC and its headphone jack is not going to produce hifi sound, but on the other hand, for out-of-the-box computer sound, that G4 sounds darn good. You should not be experiencing any overt distortion like you describe.

Please try one thing: Play some of your music files through QuickTime on your iMac (don't even launch iTunes). If the music sounds clean when played through QT, you have a software issue that I may be able to help you with.


You're right, playing the songs directly through the QuickTime player eliminates the problem. The sound is quite different, much cleaner. I really would appreciate your advice about the software issue.
Sfar, here's one thing to try (hope it works--I don't know another thing to try). BTW, if you can play the same files through iTunes from another user account without distortion, this almost certainly is the problem.

The iTunes preference file can get corrupted, and this can lead to distorted playback (I have no idea why this is!). With iTunes closed, go to the Library folder in your user folder, open the Preferences folder and look for the "" file. Drag it to the Desktop (you can Trash it later, if this fix works). Start up iTunes, and it will build itself a new preferences file. Play music, and hopefully the sound quality will be restored to normal.

You may have to reset some of your preferences--be especially sure that your iTunes Music Folder Location is set properly to avoid surprises as you add files to your collection in the future. Your existing music library and playlists will not be affected at all by trashing the preferences file.

Hope this works for you.
Jayboard, dumping the preference file worked! Thanks a lot.

Back when I was running systems under OS 9, tossing the preferences file was almost routine when troubleshooting any application problem but it had never come up for me under OS X and it would never had occured to me that audio output quality might be connected to a corrupt preferences file.

There was a second file in the preferences folder that I took out at the same time,, which I assume contains the software equalizer preferences. I'd been wondering if the equalizer settings were part of the problem, even before your suggestion. I don't know which file it was that was causing the problem but now it's working quite well.

Your solution saved me a lot of time and probably some money since I don't feel compelled to race out and try a digital-out solution. I'll probably try something like the Waveterminal eventually but, for now, things sound great.

Thanks again, I really appreciate your help.
Sfar, that's great! Yes, it's baffling why the preferences file would affect sound quality. iTunes is a strange and wonderful beast.
An update on fixing the problem:

After the original fix in which I deleted both iTunes preference files I began to use iTunes again, including changing settings in the software equalizer. The problem returned.

This time I deleted only the equalizer preferences file, the one named "", without touching the """ file.

When I restarted iTunes the problem was gone so it's clear that, at least in my case, it's the use of the equalizer and the corruption of its prefereces file that is creating the distortion problem.